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Caulerpa taxifolia

From Biocrawler, the free encyclopedia.

Caulerpa taxifolia

Scientific classification

Kingdom:	Protista
Division:	Chlorophyta
Class:	Ulvophyceae
Order:	Caulerpales
Family:	Caulerpaceae
Genus:	Caulerpa
Species:	C. taxifolia

Binomial name

Caulerpa taxifolia
(M. Vahl) C. Agardh, 1817

Caulerpa taxifolia is a species of seaweed (a type of algae) that has been commonly used as ornamentation in aquarium installations around the world. The algae was found to thrive in cold aquarium environments by the staff at the Wilhelmina Zoo in Stuttgart, Germany in 1980. It appears that, in 1984, the seaweed was accidentally released into coastal waters of the Mediterranean Sea just below the Oceanographic Museum of Monaco. By 1989, the species had grown to cover a large area and was preventing other plants from growing, leading to the nickname "Killer Algae". The plant began to spread between ports along the Mediterranean coast. C. taxifolia has been discovered off the coasts of Australia and the United States, though none of those encroachments have been anywhere near the scale of what is happening in the Mediterranean.

For several years, the origin of the species was unclear. Marine biologist Alexandre Meinesz first discovered the plant in the 1980s, and requested the help of the Monaco Oceanographic Museum, which sat right next to the first known taxifolia patch. However, the director of the museum argued that this invasion probably happened naturally, the result of ocean currents carrying a tropical species into the area. Bickering over whether the species was natural or invasive, and whether the museum had released it or not, contributed to a delay that allowed the plant to spread beyond control. The museum continued to deny releasing the plant, although former director Jacques-Yves Cousteau eventually expressed the belief that it was the only reasonable explanation.

C. taxifolia has no natural predators or competitors in the Mediterranean. It crowds out other fish and plants, and contains a strong toxin that is distasteful to most species around the world. Regions that have been invaded by the plant now show that about half the expected number of fish have disappeared.

The algae has a stem which spreads horizontally just above the seafloor, and out of this stem there grow vertical fern-like pinnae, whose leaves are flat like yew, hence the species name "taxifolia" (the genus of yew is "taxus"). The algae produces within it a lot of a single special kind of poison, which repels fish and other would-be predators. This is in contrast to other plants which produce a variety of toxins, but in reduced amounts. In addition, the aquarium strain is less susceptible to the colder temperate waters of the Mediterranean as are the naturally occurring tropical varieties.

The aquarium strain reproduces asexually, that is, vegetatively: the viscous, elastic white fluid inside the stem was found under the microscope to contain only male gametes. Rate of growth can be as fast as a centimeter per day. If any small part is severed from the rest of the algae, this small part will regrow into another algae. This means that infestations of the aquarium strain of Caulerpa can metastasize easily to other areas of the sea. Anchors of ships and fishing nets can serve as carriers of Caulerpa. Thus the algae infestations have been found to jump from the coast of one port city to the coast of another port city: from the coast of Monaco to the southern coast of France, the coast of Sicily, jumping to the other side of Italy into the Adriatic Sea off the Balkan coast...

In 2000 the strain was found in the coast of California (U.S.A.), near San Diego, and also in the coast of New South Wales, Australia. The California invasion was small enough to be considered controllable: it was covered with tarpaulin which was held down with sandbags at the edges of the infestation. Then chlorine was poured in through tubes which fed into certain openings in the tarpaulin: the interior of the tarpaulin fills up with chlorine and kills living organisms inside it, including the killer algae but also fish and plants. The killing of such other organisms was not desirable but was deemed preferable to letting the weed grow unchecked, which would in the end yield greater havoc on these same creatures.

The invasion in the Californian coast was most probably caused by an aquarium owner improperly dumping the contents, allowing C. taxifolia to flow through a storm sewer into the lagoon where the invasion was discovered. California has since passed a law forbidding the possession, sale or transport of Caulerpa taxifolia within the state. There is also a federal law under the Noxious Weed Act forbidding interstate sale and transport of aquarium strain Caulerpa.

Researchers in the University of Nice in France have been studying a tiny aquatic slug, similar to a snail but without a carapace on its back, which is known to be a natural predator of C. taxifolia. Called Elysia subornata, It was found off the coast of Florida, whose waters are warmer than those in the Mediterranean. Mediterranean waters are so cold in winter that they would kill this slug, but not the killer weed. This slug is believed to feed exclusively on Caulerpa taxifolia, by sticking its proboscis into the stem and sucking out the white viscous liquid inside the stem: this causes the algae to become limp, discolored, and dead. As the slug does so, it absorbs the algae's poison. The slug has an enzyme which neutralizes the noxious effect of the poison, and at the same time the poison protects the slug from being eaten by fish. This slug has not yet been used to check the growth of killer weed in the Mediterranean.

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